The Program Project on Reactive Species in Vascular Injury will examine the role of reactive species, including superoxide (02-), hydrogen peroxide (H202, hydroxyl radical (.OH), nitric oxide (.NO) and secondary reaction products such as peroxynitrite (ONOO-) in the pathogenesis of vascular injury. These reactive species, sometimes termed free radicals, serve a beneficial role in tissue processes such as bacterial killing, the maintenance of vascular tone and inhibition of platelet aggregation. The pathogenic mechanisms of diverse vascular disease processes include significant but often poorly defined contributions from reactive oxygen and nitrogen species. We propose to use multidisciplinary approaches to better understand and prevent free radical injury in important clinical situations. This includes: a) the oxidative modification of lipoproteins and the abnormal vasoregulation which occurs in atherosclerosis; b) the ischemic tissue injury induced by transplantation; c) the organ damage ensuing from aortic crossclamping during vascular operations, and d) the myocardial injury that occurs during cardiac operations. Project 1 investigates the production of toxic molecules generated from the reaction of endothelial-derived relaxation factor (.NO) with 02- and examines the role of these species during animal and human myocardial ischemia-reperfusion. Project 2 studies circulating xanthine oxidase released into the circulation and secondary systemic effects occurring after diverse forms of organ ischemia, such as experienced during transplantation and vascular surgical procedures involving aortic crossclamping. Project 3 defines mechanisms of vascular endothelial cell oxidant metabolism, focusing on the unique interactions of circulating xanthine oxidase with cell surface binding sites and the interplay between cellular 02- and .NO in the formation of secondary toxic species. Project 4 win examine molecular signaling mechanisms in vascular cells of normal and hypercholesterolemic animals to better understand mechanisms of atherogenesis, the role of oxidants and the causes of impaired blood vessel function in atherosclerosis. These four projects are supported by administrative, cell culture and bioanalytical core units. This integration of basic and clinical endeavors will rapidly advance understanding of pathogenic mechanisms and the diagnosis and treatment of key problems in vascular medicine, including atherosclerosis, ischemia-reperfusion injury (i.e., heart attack and stroke), organ transplantation and abnormal vasoregulation.